Alkylation process



complish the desired separation.

States .Patent o 12,946,832" o .Arrestation Pnocnss .The `Standard Oil,Companyg Cleveland, Ohio, a corporation of )ho t v Filed May 14, 195s,ser. No. .735,205I

. fz claims. (cl. 1to1-razas) after-merely for fthe @purposes ofillustration, audit motatobe :construed :as -a limitation on the'scopeof-athe invention. Y o Y conventionally pra'cticed, thel .alkylation"lprocessais `usually conducted :at llow temperatures (about .140? in'the presence of-'aetrong1 mineral acid catalyst, "ezgl,

or.;hydrofluoric acid; The manner of conducting the'process `andthe1conditions" at which optimum'tesults .are obtained :are all well.-lcnown tto/those skilled inf the fart; Ordinari-1y, the .feed totheprocess is amixturerof ation process inview ofet-he n -parafrlncontentV since it is primarily only the iso-para-ns which` willalkylate.

ilighthydrocarbonssuchas that producedfin norrrra1re ,dining operationsand it usually contains varying amounts -ofnormal gparafnslisofparafns,and olei'ns.l However,

:such'mixtures are not :the most desirable. feed ttoa1-1-ailcy-l4v 40The' normal parains-,donot react to any appreciable extent andservemerely vasv diluents in the reaction mixture. Y'

yIt .isknown that :the .bestrresults .are obtained in an alkylation.reaction whenv thev iso-paraiiins are present in a substantial` molalvexcess ,asl compared to v.the olens. .Since the ,streamsavailable :inVthereiinery ras feed to the `alkylation processVv cio-,not ordinarilycontain the desired .substantial excess. of.V iso-parains, it iscustomary to .separate unreacted iso-parans. from-the reaction-products.:and ,recycle vthem yto theY alkylation reacton Asmentionedtheretofore,alkylation feedfwill ordinarily contain .non-reactive normal tparains,aswell as reactive iso-parains, and these appear in the eiiiuent fromthe -al- 'kylation reactor. Consequently, the n-parains mustlbeseparated from .the iso-parans before the iso-parai-ns are ,recycle ,to.the reactorsince, otherwise, the normal paraffins would tend` toaccumulate gradually within .thereactor system. This separation isdifficult because of the close proximity of the boilingpoints of thenormal paraffns and the isoipa'rans and', heretofore, ithas beennecessary to resort toexpensivedistillation equipment to ac- A perfectseparation ofthe n-'paraifns` from 'the' iso-'paraiiins is impracticalwith conventional distillation equipment and consequently a substantialquantityofn-parains are circulated within the alkylationsystem;

Accordingly, it is the object of this invention to provide means forobtaining a more perfect separation of the normal parans from theiso-paraffins which are Vrnoleoular sieves.

Vtion of normal parans.

The molecular sieve beds may be desorbedby a num ffice intended tocomplement conventional distillation` facilities. 'More "specifically,the objectof this inventionis to obtain-a relatively pure iso-'parainvstream i'for V-re'cycle to the alkyl'ation reactor so :as 'to lavoidthe recycle of fn-parain's tto thebreactor. Y

.n '.brief,:1he `process r4of my invention comprises a conwentional`alkylation system 2in which' the reactor euent V'is subjected to apreliminary distillation :step 'to' remove n stream .consistingessentially fof fisoparaf-ns Sand a minor proportion of Yn-pal-"aflinsThis stream .is next contacted with a ined comprising a `special classof inorganic adsorbent which yselectively removes `the n-par- Aafhns.VThe yeliiuent nfrom the 'adsorption ,Zone lconsisting `.essentially 'ofisoparatlns'visftheu recycled to the alltylation reactor. The bed of'adsorbentfmaterial is periodically regeneratedgto remove then-para'ins.

The adsorbent bed employed Vin this 'process 'is composed-of especialclass of inorganic adsorbents known as Molecular Sieves are vsynthetic-zeolites manufactured .in Vsuch a manner :as to have controlled specicjporosity. The molecular sieves adsorb the normal ,paraffins by amechanism :of exclusion Molecules whose diameters are vsmaller than`Ythe :pore openings of the ysieves will enter `the pores `and therebybecome adsorbed. while molecules .having diameters `lar-ger than thepores willl be rejected 'by the Sieves.

Sieves are avail-able in several 'pore sizes 'bu-t for my purposewlprefer a'y sieve' havingpore openings of about 5 A. since this size willadso-rb normal butano and'reject `paraiflins'may be accomplished -byrcontacting the hydrocarbon-feed mixture in either liquid lor 'vaporphase with 'an-adsorption bed, but theoperation-is* preferablyconducted-inthe vapor phase. rifhetemperature-d-uiing the adsorption inthe vapor phasemay range froml 100 to 150 F. and the pressure from v85to 125v p.s.i.g.- The lower temperatures land higher pressures-avorvtheadsorpber of methods which are well known to those skilled in theHowever, I prefer to desorby the :bedsby reducing the pressure zandraising the bed temperature ysince this proceduregprecludes theintroduction of. ex-

, traneous material in .the lallkylation system.

The process for this invention will be better understood by reference tothe attached patent ldrawing which presents in schematic form theprocess of the invention, and ra discussion of this'drawing now follows:

A renery gas stream comprising butylenes, iso-butane, and n-butanetogether with recycle isobutaues, the source of which is describedhereinafter, is introduced through line Y1 into y-a conventionalIauto-refrigerated alkylation reactor 2, wherein the `isoA-butane andbutylenes react. After treatment to kremove residual acids, the reactoreiiuent flows through line 3 to a. deisofbutanizer 4 where amixturecomprising iso-butane'and a significant quantity of normal butane'isremoved overhead through line 5. 'Y v The bottoms from thedeisobutani'zer4 are sent through line 32 to the debutanizer 30 Wherenormal butane is taken overhead through line 31, condenser 38, and areflux drum 26. A part of the condensate is reuxed to the debutanizerthrough line 27, valve 28, and line 29, the remainder being sent tobutane storage through line 34. The bottoms product from the dcbutanizer30 is known as alkylate and this product is sent from the plant throughline 33, either directly to storage, or it may be subjected to furtherfractionation (not shown).

Theoverhead stream from the deisobutanizer tower 4 comprising iso-butaneand some normal butane is passed.V through line 5, valve 6, to theadsorbent bed 7. Normal butane is adsorbed on the Vbed and the effluentis relatively pure iso-butane which is conducted through line 8, valve9, line 10, condenser 37 to reux drum 11.

The adsorbent lbeds 7 and 18 are arranged in such a manner so as tosupply a steady stream of iso-butane to reiiux drum 11. While adsorbentbed 7 is on an adsorbing cycle, as heretofore described, adsorbent bed18 is subjected to a desorption cycle. In order to switch the feed frombed 7 to bed 18, valves 6, 9, 21 are closed and valves 16, 20, 24 areopened.

Adsorbent bed 7, when it becomes loaded with normal butane, is desorbedby closing valves 6 and 9, opening valve 24, depressuring molecularsieve bed 7 and heating the `bed 7 by passing steam through steam coil36. The n-butane is removed through line 3, valve 24, line 25, condenser39, into reflux drum 26.

Adsorbent bed 1Sl is loaded and desorbed in the same manner. The.relatively pure iso-butane which accumulates in the reflux drum 11 isreturned through line 15 to line 1, and finally to the alkylationreactor 2.

An example of the preferred embodiment of my invention now follows:

4,000 barrels per day of a refinery gas stream is fed to the alkylationreactor. This stream had the following composition: l

Component: Vol. percent C3 3.0 i-C4 42.0 lil-C4 C4= 35.0 C 5.0

In addition, 6360 barrels per day of iso-butane were continuouslyrecycled to the reactor. The reactor was maintained at a temperature of40 F. and a pressure of l0 p.s.i. The catalyst employed in the reaqmrwas 92.0% sulfuric acid.

The reactor efuent, Yafter the customary cleanup, was transferred to adeisobutanizer containing 50 trays which was operated zat a pressure ofV100 p.s.i.g. and at a reboiler temperature of 240 F. 7500 barrels perday Were taken as the overhead product from the deisobutanizer and thisstream had the following composition:

Percent Iby volume iso-Butane 85 n-Butane 15 3100 barrels per day wereremoved from the bottom of the deisobutanizer and this stream wascomposed at 2450 barrels per day of alkylate and 600 barrels per day ofn-butane (50 barrels of residual i-butane).

The overhead stream from the deisobutanizer was transferred in the vaporphase to a vessel containing 125,000 lbs. of a synthetic zeoliteadsorbent having an average pore opening of about 5 angstroms. The vaporcomprising relatively pure iso-'butane issuing from the adsorber wascondensed by conventional means and 10,000 barrels per day of thecondensate were recycled to the alkylation reactor with the remainderbeing employed as reflux to the deisobutanizer. During thisoperation,the bed of adsorbent material was maintained'at a temperatureof 130 F. and at a pressure of 95 p.s.i. After 6 hours of continuousoperation, the adsorption bed became loaded as evidenced by theappearance of n-butane in the vaporous product issuing from the vessel.At this time, the overhead from the deisobutanizer was switched toanother and similar vessel containing adsorbent material and theconditions of the vessel containing the loaded adsorbent were adjustedto a temperature of 350 F. and a pressure of p.s.i. The latter change inconditions resulted in the desorption of the adsorbent material and atotal of 50 barrels of n-butane were Vrecovered lby this step. Thedesorbed adsorbent was then subjected toianother cycle with feed fromthe deisobutanizer overhead with similar results.V f I Thus, it can beappreciated that the process of the invention hasa number of advantagesover the yconventional process. One of these is that the processproduces a relatively pure iso-butane stream which may -be employed `asrecycle to the alkylation reactor and as reflux in the deisobutanizer.Elimination ofthe n-butane from the recycle/stream improves thealkylation reaction since a useless diluent is eliminated, and; at thesame time, the capacity of the reactor isincreased by an'amount equiv-`alent to the amount of n-butane removed from the recycle stream.Furthermore, the elimination ofn-butane from the reflux to thedeisobutanizer increases the sepa ration efliciency of that tower.

=I claim:

1. An alkylation process comprising the steps of contacting a normallygaseous hydrocarbon mixture comprising iso-alkanes, olefins andn-alkanes with a catalyst in a reaction zone under alkylationconditions, withdrawing a mixture of product land unreacted feedmaterial from. said reaction zone, introducing said mixture of productand unreacted feed material into a distillation zone and adjusting thetemperature and pressure in said distillation zoneso as to separate amixture comprising substantially all of the iso-alkanes and a partof then-alkanes from said mixture, passing said mixture of'iso-alkanes andnalkanesA to an `adsorption zone containing a bed of molecular sieveshaving an average pore size of about y5 angstroms and recoveringtherefrom a stream consisting essentially of iso-alkanes, and nallyreturning at least part of said iso-alkane stream to said distillationzone as reflux and recycling the remainder of said iso-alkane stream tosaid reaction zone. Y 'Y 2. An alkylation process comprising the stepsof contacting a normally gaseous hydrocarbon'mixturel compris- Vamixture of product Vand unreacted feed material from said reaction zone,introducing said mixture of product and unreacted feed material into adistillation zone and adjusting the temperature and pressure in saiddistillation zone so as to separate -a mixture comprising substantiallyall of the iso-butane and ra part of the n-butane from said mixture,passing said mixture of iso-btuane and n-butane to an adsorption zonecontaining a bed of molecular sieves having an average pore size ofabout 5 angstroms and recovering therefrom a stream consistingessentially of iso-butane, and finally returning at least part of saidiso-butano stream to said distillation zone as reflux and recycling theremainder of said iso-buttane stream to said reaction zone.

References Cited in the tile of this patent UNITED STATES PATENTSBallard et al. Dec. 3l, 1957

1. AN ALKYLATION PROCESS COMPRISING THE STEPS OF CONTACTING A NORMALLYGASEOUS HYDROCARBON MIXTURE COMPRISING ISO-ALKANES, OLEFINS ANDN-ALKANES WITH A CATALYST IN A REACTION ZONE UNDER ALKYLATION CONDITION,WITHDRAWING A MIXTURE OF PRODUCT AND UNREACTED FEED MATERIAL FROM SAIDREACTION ZONE, INTRODUCING SAID MIXTURE OF PRODUCT AND UNREACTED FEEDMATERIAL INTO A DISTIALLATION ZONE AND ADJUSTING THE TEMPERATURE ANDPRESSURE IN SAID DISTILLATION ZONE SO AS TO SEPARATE A MIXTURECOMPRISING SUBSTANTIALLY ALL OF THE ISO-ALKANES AND A PART OF THEN-ALKANES FROM SAID MIXTURE, PASSING SAID MIXTURE OF ISO-ALKANES ANDNALKANES TO AN ADSORPTION ZONE CONTAINING A BED OF MOLECULAR SIEVESHAVING AN AVERAGE PORE SIZE OF ABOUT 5 ANGSTROMS AND RECOVERINGTHEREFORM A STREAM CONSISTING ESSENTIALLY OF ISO-ALKANES AND FINALLYRETURNING AT LEAST PART OF SAID ISO-ALKANE STREAM TO SAID DISTILLATIONZONE AS REFLUX AND RECYCLING THE REMAINDER OF SAID ISO-ALKANE STREAM TOSAID REACTION ZONE.